Variable band coupling device for superheterodyne radio receivers



Aug. 17, 1937. H. J. LYMAN VARIABLE BAND COUPLING DEVICE FORSUPERHETERODYNE RADIO RECEIVERS 2 sheets-Sheet 1 Filed Aug. 5, 1935 m/WOW l.. OPF (Q /Lts MJ FREQUENCY lu" (/LGCYCLES OFF RESONACE Harry/41gwww H. J. L YMAN 2,090,538

VARIABLE BAND COUPLING DEVICE FOR SUPERHETERODYNE RADIO RECEIVERS Aug.17, 1937.

2 Sheets-Sheet 2 Filed Aug. 5, 1935 2 No DETEC Toe ff' AMPL/F/E/Q srDETEcTo/a 2` AUTOMATIC VOLUME CONTROL C/Z CUIT FREQUENCY /N KILCYOLESDFF /QESNANCE w d 6 mmm www Q@ Patented Aug. 17, 1937 narrar oFFlcEVARIABLE BAD CUPLING DEVICE FOR SUPERHEIIVERDYNE RADIO RECEIVERS HarryJ. Lyman, Philadelphia, Pa., assignor to Philadelphia Storage BatteryCompany, Philadelphia, Pa., a corporation of Pennsylvania ApplicationAugust 5,

1935, Serial No. 34,809

In Great Britain September 25, 1934 Claims.

This invention relates to coupling devices for electrical circuits andis particularly adapted for use in superheterodyne radio receivers. Thegeneral object of the invention is to provide a novel v5 transformer orcoupling device in which the frequency response or band width may bevaried. As is well known, in superheterodyne radio receivers the extentof the audio frequency range of the receiver is determined by the bandwidth of the 10 intermediate frequency system as well as by otherfrequency selective systems which may be incorporated in the receiver.In order to obtain high fidelity response it is necessary to providemeans by which the side bands of the modulated carrier "'15 wave signalmay be transmitted Without being markedlyv attenuated. The inventionprovides means for broadening the response so as to obtain high idelity,at the same time maintaining the gain of the receiver substantiallyuniform.V

A further object of the invention is to provide a circuit by which thefidelity curve or response curve of the receiver may be varied manuallywithout the use of expensive or complicated parts. The invention may befully understood from the following detailed description in connectionwith the illustrative embodiments of the accompanying drawings. In thedrawings:

Figure 1 is a schematic illustration of a simple circuit employing thenovel features oi' the invenformer 'I' embodying the features of theinvention,

as will be fully described hereinafter. The tube V1 may be energized bya suitable source oi' electrical waves or oscillations E. This sourcemay take the form of any suitable signal source.

The transformer T comprises a primary winding L1 and a secondary Windinginductively coupled thereto comprising portions L2 and L3, the purposeof which will be clearly-understood from l the subsequent description.`'I'he primary winding L1 is included in the output circuit of the tubeV1, while the secondary winding L2, L3 is included Fig. 2 illustratestypical response curves which (Cl. LYS- 44) inY the input circuitl oftube V2 in conventional manner. A condenser or capacitance C1 isassociated with the primary Winding L1, one side of the condenser beingconnected directly to an extremity of the primary winding as at I, whilethe other 5 side of the condenser is connected to the movable contact 2of a switchS. The switch S also comprises stationary contacts 3 and 4arranged for selective engagement by the movable contact 2. Thestationary contact 3 is connected to a point 10 5 of the secondarywinding, which point divides the said winding intothe portions L2 andL3. A condenser C2 is connected across the secondary winding inconventional manner.

The extremity of the primary winding L1 opposite the point l may beconnected to ground through a blocking condenser C3 and thecorresponding extremity of the secondary winding may be likewiseconnected to ground through a blocking condenser C4. preferred, it willbe understood that an alternative arrangement may be employed in whichthe extremities in question of the transformer wind-. ings are connectedtogether through a single blocking condenser. 5

It will be seen that when the movable contact 2 of switch S is inengagement with the stationary Contact d, the circuit comprises aconventional tuned transformer circuit and, if the inductive couplingbetween the transformer windings is 30 critical or slightly less thancritical, the fre quency response or transmission characteristic of -thesystem will be substantially as illustrated by kthe frequency responsecurve 6 of Fig. 2. When the movable contact 2 of switch S is inengagement with the stationary contact 3, however, the, portion La ofthe secondary winding is included in circuit with the condenser C1 andthe inductive coupling between the two windings is increased by anamountcorresponding to the inductance of portion L3 which is common to bothwindings. In other words, the degree of coupling between the tunedprimary and secondary circuits is increased and the said circuits are,at the same time, de tuned to a limited extent.` The frequency respenseor transmission characteristic of the systern is now substantially asshown by the frequency response curve 1 of Fig. 2. `It will beunderstood that the dividing point of the second-V ary winding may bechosen torgive the desired 50 response characteristic. v

It will be noted that the broader response curve 'l has two peaks spacedon opposite sides ofthe peak of the Aoriginal curve 6, there'being aslighti depression between the two peaks. -i In order that` While thisarrangement is 20 where Mlzzmutual inductance in henrys between theprimary winding and the portion L2 of the secondary winding M13=mutualnductance in henrys between the primary winding and the portion L3 ofthe secondary winding S turns in whole secondary turns in primary L1 andL2 are the self inductance in henrys of the primary winding and theportion L2 of the secondary winding, respectively.

lWiththis condition existing, the peak spacing may be defined in termsof the circuit characteristics as follows:

1 Peak spacing=ml Ml3 +1/L1L2) cycles fzfrequency in cycles to which theprimary and secondary circuits are resonant each in the absence of theother C1=capacity of condenser C1 in farads.

These results have been derived under the assumption that the resistanceof the circuits may be neglected except insofar as they are necessary inorder to determine critical coupling, and further that for the kpositionof minimum band width, the primary and secondary circuits will be tunedto the. same frequency, and that the primary and secondary will be lessthan critically coupled.

For the case in Which these relations are not satisfied there will be aslight band displacement to one side or the other. It has been found,however, that this displacement is relatively slight and will not beobjectionable. Consequently, if desired more than Ytwo taps may beplaced in the secondary and several degrees ofband width may CsiA beobtained. The curves shown in Fig. 2 represent the case wherein thesecondary winding comprised 400 turns of wire tapped at the th and 20thturns up from the bottom. In this particular case, the response curves 6and 8, corresponding to minimum and intermediate band Width, wereadjusted according to the above formula and were symmetrical within thedegree of precision of the measurements. The third curve 1, taken withthe condenser C1 connected to the 20th turn tap, was displaced from thesymmetrical position by an amount corresponding to about 4 percent ofthe band width.

While the invention is directed particularly to superheterodyne radioreceivers as above stated, the features of ythe invention illustrated inFigs. 1 and 2 of the drawings, are capableof general use. In otherwords, in its broad aspect, the invention is directed to electricaltransmission systems and is, therefore, to be so considered.

In Fig. 3, the invention is illustrated as applied to a conventionalsuperheterodyne radio receiver.

In this specific` illustration, there is shown a portion of the firstdetector stage, an intermediate and I3 on the associated secondarywinding.

frequency stage, and a portion of the second detector stage. It will beunderstood, of course, that the intermediate frequency portion of thereceiver may'comprise one or more Vacuum tube stages, as is Wellunderstood, and the detector stages may be varied in accordance withknown practice. It will be also understood that the usual antennacircuit may be providedand conventional radio and audio frequencyamplifiers each comprising one or more stages may be employed, and asound reproducing device may be connected to the output of the system,although these conventional elements are not shown. v

Following the teachings of the invention, there are provided tunedtransformers T1 and T2 which are generally similar to the transformer Tof Fig. 1. Selective switches S1 and S2 are associated respectively withthe transformers T1 and T2. In order to provide three degrees offidelity of the receiver, each of the switches S1 and S2 comprisesstationary contacts 9, I0, and II, the contacts I0 and II beingconnected respectively to points I2 The switches S1 and S2 may beadapted for simultaneous or` tandem operation in conventional manner, asindicated by the broken-line representation.

When the switches are adjusted to the contact position 9, minimum bandwidth is provided, as will be understood from the foregoing description.Adjustment of switches Si and S2 to the contact positions I0 and IIselectively increases the fidelity from the minimum to the maximum. It

will be understood that the device provided by the invention may beemployed to couple each of the stages of the intermediate frequencyamplifier, as well as to couple the said amplifier to the detectors, orto couple the detectors to each other.

It should be borne in mind that the frequency response or transmissioncharacteristic of each of the portions of the receiver other vthan theintermediate frequency portion should be suciently broad so as not toreduce the over-allV frequency response of the receiver when adjustedfor maximum fidelity. In otherwords, assuming a maximum frequencyresponse such as illustrated by curve I of Fig. 2, the frequencyresponse of each of the said other portions of the receiver should bebroader than the response curve l. In general, this condition is`satisfactorily met in practice using conventional elements in the saidother portions of the receiver but, if necessary or desired, the deviceof the present invention, as illustrated in Fig. 1, may be used in otherportions of the receiver to obtain the requisite breadth of frequencyresponse.

The conventional radio frequency amplifier comprising one or more stagesusually has a frequency response or transmission characteristic such askillustrated by curve I4 of `Fig.' 4. This response curve is generallybroader than the response curves shown in Fig. 2 and has a broad peakcoincident with the central depressions in the curves I and 8 of Fig. 2.When the receiver is adjusted for increased fidelity to give a responsesuch as illustrated by the curves l and 8 of Fig. 2, the over-allresponse of the receiver will be substantially asv illustrated by thecurve I5 of Fig. 4 which represents the resultant of the response of theradio frequency stages and the intermediate frequency stages. It will beseen that the central depressions of the response curves I and 8 aresubstantially balanced out.

by the peak of the curve I4 so that the over-all crest. Thus theover-all gain of the receiver is maintained substantially uniform.

Automatic volume control may be incorporated in the receiver asillustrated in Fig. 3. The volume control voltage may be derived from asuitable source, such as the input circuit of the second detector, andmay be applied to one or more of the preceding ampliner stages.

VAlthough the invention has been .illustrated and described withreference to certain specific embodiments for the purpose of disclosure,it will be understood that various changes and modifications may be madewithout departing from the spirit and scope of the invention, and thatthe invention is capable of broad adaptation as above stated.

I claim: Y

1. In a tuned coupling device, the combination of an inductivereactance, a capacitive reactance having one connection in common withsaid inductive reactance, said reactances comprising a tuned circuit, asecond inductive reactance, a second capacitive reactance having oneconnection in common with said second inductive reactance, said lastnamed reactances comprising a second tuned circuit, said rst tunedcircuit and said second tuned circuit being coupled one to the other,low impedance means connecting said rst tuned circuit and said secondtuned circuit, and switching means for effectively including a selectedportion of a reactance of one of said tuned circuits in circuitv with areactance of the other of said tuned cricuits, to thereby simultaneouslyvary the tuning of and coupling between said circuits. Y

2. In a tuned coupling device, the combination of `an inductivereactance, a capacitive reactance having one connection in common withsaid inductive reactance, said reactances comprising a tuned circuit, asecond inductive reactance, a second capacitive reactance having oneconnection in common with said second inductive reactance, said lastnamed reactances comprising a second tuned circuit, said first tunedcircuit being electromagnetically coupled to said second tuned circuit,low impedance means connecting said rst tuned circuit and said secondtuned circuit, and switching means for effectively including a selectedportion of a reactance of one of said tuned circuits in circuit with areactanc-e of the other of said tuned circuits to thereby simultaneouslyvary the tuning of and coupling between said circuits.

3. In a tuned coupling device, the combination of an inductivereactance, a capacitive reactancev having one connection in` common withsaid inductive reactance, said reactances comprising a tuned circuit, asecond inductive reactance, a

second capacitive reactance having one connection in common with saidsecond inductive reactance, said last named reactances comprising asecond tuned circuit, said iirst tuned circuit and said second tunedcircuit being resonant to substantially the same frequency and beingcoupled one to the other, low impedance means connecting said rst tunedcircuit and said second tuned circuit, and switching means foreffectively including a selected portion of a reactance of one of saidtuned circuits in circuit with a reactance of the other of said tunedcircuits, to thereby simultaneously vary the tuning of and couplingbetween said circuits. Y

4. In a tuned coupling device, the combination of an inductivereactance, a capacitive reactance having one connection in common Withsaid inductive reactance, said reactances comprising a tuned circuit, asecond inductive reactance, a second capacitive reactance having oneconnection in common with said second inductive reactance, said lastnamed reactancesV comprising a l second tuned circuit, said first tunedcircuit andV said second tuned circuit being resonant to substantiallythe same frequency and being electromagnetically coupled one to another,low im-Y pedance means connecting said rst tuned cirf cuit and saidsecond tuned circuit, and switching means for eiectively includingaselected portion of a reactance of one of said tuned circuits incircuit with a reactance of the other of said tuned circuits, to therebysimultaneously vary the tun- C.

ing of and coupling between said circuits.

5. In a tuned coupling device, the combination of an inductivereactance, a capacitive reactance having one connection in common withsaid inductive reactance, said reactances comprising a"4 f tunedcircuit, a secondinductive reactance, aV Y econ'd'capacitive reactancehaving one connection in common with said second inductive reactance,said last named reactances comprising a second tuned circuit, said firsttuned circuit and said second tuned circuit being coupled one totheoth-er, low impedance means connecting said rst tuned circuit 'and saidsecond tuned circuit, and

switchingmeans for connecting a reactance of one of said tuned circuitswith one of a plurality of tapped points of a reactance of said other.

tuned circuit, said rst tuned circuit being electromagnetically coupledto said second tuned circuit, low impedance means connecting said firsttuned circuit and said second tuned circuit, and switching means forconnecting a reactance of one of said tuned circuits with one of aplurality of tapped points` of a reactance of said other tuned circuitto'include the former reactance in circuit with a portion of the latterreactance in at least one switch position and to thereby simultaneouslyvary the tuning of and coupling between said circuits.

7. In a tuned coupling device; the combination of an inductive Winding;a second inductive winding coupledto said first winding; a connection,having a low impedance at the operating frequency, between an end of oneof said windings and an end of the other of said windings, whereby a lowimpedance path at said frequency is provided between said windings; acapacitive element in shunt with said second winding and forming a tunedcircuit therewith; a second capacitive element having one side thereofconnected to the other end of said first 'windingl and forming therewitha second tuned circuit; and switching means for connecting the otherside of said second capacitive element to selectable points associatedwith said second winding, for including not more than a minor portionofsaid second lwinding in circuit with said first winding, to

thereby simultaneously vary the tuning of and coupling between saidcircuits.

8. In a tuned coupling device; the combination of a tuned transformerincluding a rst inductive winding and a second inductive winding coupledthereto; a connection, having a low impedance at the operatingfrequency, between an end of one of saidV windings and an end of theother of said windings, whereby a low impedance path at said frequencyis p-rovided between said windings; a capacitive element in shunt withsaid second winding and forming a tuned circuit therewith; a secondcapacitive element having one side thereof connected to the other end ofsaid first winding and forming therewith a second tuned circuit; andswitching means for connect- Ving the other side of said secondcapacitive ele- Y ment to selectable tapped points on said secondwinding, for including not more than a minor portion of said secondwinding in circuit with said first winding, whereby a selected minorportion of said second winding may be included inY s circuit with saidrst winding to thereby simulthereof connected to the other end of Saidfirst winding and forming therewith a second tuned circuit; saidwindings and their respective associated capacitive elements comprisingtuned circuits which are resonant at substantially the same frequency;and switching means for connecting the other side of said secondcapacitive element to selectable tapped points on said second winding,for including not more than a minor portion of said second winding incircuit with said first winding, whereby a selected minor portion saidwindings and an end of the other of said windings, whereby a lowimpedance path at said frequency is provided between said windings; acapacitive element in shunt with said secondary winding and forming atuned circuit therewith; a y condenser having one side thereof connectedto' theY other end of saidprimary winding and forming therewith a secondtuned circuit; and switchrneans for connecting the other side of saidcondenser to selectable tapped points on saidsecondary winding, forincluding not more than a. minor portion of said secondary winding incircuit with said primary winding, whereby a selected minor portion ofrsaid secondary windingrv may be included in circuit with said primarywinding to thereby simultaneously vary the tuning of and couplingbetween said circuits.

f kHARRY J. LYMAN.

